Process for refining gold.



Empire,

cnuoo UNITED strAT s Li LitimitiJts PATENT OFFICE.

HEINRICH WOHLWILL, 0F HAMBURG, GERMANY, ASSIGNOR TO THE FIRE OFNORDDEUTSCHE AFFINERIE,

'OF HAMBURG, GERMANY.

PROCESS OF REFINING GOLD;

961,924. No Drawing.

To all whom it may concern:

Be it known that I, Hnmmon WOHLWILL, a subject of the Emperor of Germanyresiding at 31-35 Elbstreet, Hamburg, erman have invented new and usefulImprovementsin Processes of Refining Gold, of which the following is aspecification. This invention has reference to the purification 0fimpuregold, or gold alloys, and has particular reference to anelectrolytic method of producing chemically pure gold from impure goldalloys, by employing the Iianrlile as the anode in a suitableelectrolytic The present invention constitutes anv improvement on theprocesses described-and claimed in Letters Patent, Nos. 625,863 and625,864;, granted to Emil WohlWill, May '30, 1899. a

In treating gold containing a relatively large percentage of silver asthe anode in an electrolytic bath, consisting of a gold solutioncontaining free hydrochloric acid or chlorids, according to the methoddescribed in the patents above referred to, it has been found 1npractice, that when the proportion of silver in the material to berefined, exceeds six per cent, it is necessary, periodically, tomechanically remove the deposit of chlorid of silver which forms upon,and covers the anode. .Ifthis removal of the chlorid of silver isomitted, gaseous chlorin is evolved at the anode, and interferes withthe operation of the process. It has been found that the greater thedensity of the current used, and. the greater the percentage of silverin the gold anode, the sooner this condition obtains. For this reason,the process cannot be sat'sfactorily employed to purify many varietiesof gold coming from the mines, except by the use of a current ofconsiderably lower density than can be employed in the purification ofvarieties of gold containing a smaller proportion of silver. By reasonof the necessity of employing such current of lower current density, inrefining. gold containing a considerable ercentage' of silver, the oeration' is roonged, and'the removal of t e chlorid o silver from theanode materially increases the costof the process.

Now, I have found that it is possible to wholly prevent the'developmentof chlorin' Specification of Letters'Patent. Patented J 11119Applieation flled March 10,1909. Serial in. 82,476.

' sion of. the bath.

at the surface of the anode, and consequently to refine old containing avery large ercentage, 0 silver by electrolysis in materially less timeand at considerably lower expense than has been possible by the methodhereinbefore referred to, by using anasymmetrical alternating electriccurrent instead of a direct .current.

Asymmetrical currents are produced either i by commuting a directcurrent at small and unequal intervals of time, as for example,alternately every 1/50 and 3/50 seconds, or such currents may beproduced by the simultaneous use of a direct current and an alternatin'current connected in parallel. I prefer owever, to produce theasymmetrical current ina still difl'erent way, to wit by connecting asource of direct current and a source of alternating current 1n series.

This I commonly do, by connecting a direct current dynamo and analternating current dynamo in a series. It will be understood that in anasymmetrical alternating current, the curve of the current will be equalto the curve of an ordinary alternating current, but it will oscillate,not on the zero value, but on the value of the direct-current as thezero line.

' The quantitative efllect of asymmetrical currents when applied to therefining of 7 gold in accordance with the hereinbefore referred toprocess, is practically-the same as that of the. direct current alone;that is to say, the quantity of gold, dissolved the ano is practicalllated from t e strength of the direct current alone, in accordance with-Faradays law. The advantageous effect of the alternating component ofthe asymmetrical. current is however, exhibited in various ways. Forexample, as soon as the alternating current is led into the directcurrent circuit, in

which the electrolytic bath is included, the

electric tension of the bath indicated on a direct current voltameterfalls, and the greater the strength of the alternating current, thegreater the fall in the electric tenchange in their manner of'action,the ch being especially noteworthy in respect of n e r anode V By reasonof the employment of the al- Both poles exhibit a fr P de, andprecipltated at the cathode} equal to the quantity .calfcu- .ternatingcurrent with the direct current,

the latter can be considerably increased without producing an evolutionof chlorin at the'anode, consequentl the necessity of removing depositsof c lorids .from the anode is avoided.

, When currents exceed a certain limit of density, in the presentprocess, there '15 produced a slight evolution of oxygen, at the anode."This evolution is however, so insign'ificant in volume, that the loss ofcurrent produced thereby, is without importance, and such evolution has.in fact, a slightly advantageous feature in that it facilitates thefalling ofi of the deposit of-chlorid of silver which forms upon theanode. When the current denslty is materlally increased over the limitreferred to, the development of oxygen becomes greater, and'thereby the-rent is too great,

loss of c rrent becomes materla It may be here. stated, that the smallertheproportion of silver, and the higher the ratio of the alternatingcurrent to the h of the direct current, the higher current. Therefore,in the use of the asymmetrical current, the developmentot anyconsiderable amount. of gas atthe anode, as exhibited by the detachmentof more than single small bubbles from the anode, indicates that thestrength of the direct ourand the direct current must therefore, eitherbe moderated or the strength of the alternating current increased. Forexample, impure gold containing about ten per cent. of silver, accordingto the old process hereinbefore referred to, permits of no higher anodicdensity of the current than about 750 amperes to the s uare meter, andnecessitates the scraping o of deposits of silver chlorid from the anodeevery three-quarters of an hour. The

same gold, can however, be treated in accordance with the presentprocess with an asymmetrical current, the alternating component of whichhas a strength of approximately 1 to 1.1 timcs that of the directcurrent, with a density of the direct current of 1250 amperes to thesquare meter, without renderingv any scraping off of the chlorid fromthe anode necessary. The

present process also renders possible, the

treatment of gold alloys contalning a considerably larger proport1on ofsilver than can be satisfactorily treated by the use of the directcurrent alone. 'For exam le, gold containing twenty per cent. of silvercan be satisfactorily refined by the present process, by using anasymmetrical current, the

strength which is to that of the strength of the direct currentcomponent" as 1.7 is to 1, with a density of the direct currentcomponent of 1200 amperes to'the square meter. With a of the alternatingcomponent of.

somewhat lower density of the direct current component, the process canbe used for the refining of gold still richer in silver; in fact, theuse of the asymmetrical current in accordance with the present processpermits of the purification of .all classes of gold which areencountered in actual practice.

The use of asymmetrical alternating currents, and particularly the factof being able to use direct currents of high density therein, carrieswith it a still further advantage. In the electrolytic treatment of goldwith a direct current of the density commonly used in gold solutions,containing an excessive quantity of hydrochloric acid or chlorids, it isfound that about ten per cent. of the quantity of gold, of the anodes,falls in minute particles into the slimes, from which it must berecovered by a separate chemical process. When, however, theasymmetrical alternating current is used in the same situation, only a.small amountot gold falls into the slimes and this only at the beginningof treatment, when the plate has not yet been covered with silverchlorid. After this, practically no gold whatever, falls into theslimes, so that, in the operation of the present process, the-slimesconsist almost exclusively of chlorid of silver.

In as much however as a small quantity of gold falls into the slimes atthe beginning of the treatment, and some gold particles arising from themechanical isintegration of the anodes, fall into the slimes at the endof the treatment, the presence of gold in the slimes cannot be whollyavoided; but this quantity rarely exceeds one per cent. of the quantity0 if the use of currents of particularly high densities as for example,of a density in excess of 1000 amperes to the square meter, is not ofimportance, the process ofiers the signal advantage that the quantity ofhydrochloric acid or chlorids to be added to the electrolytic bath, maybe materially less than the quantity necessary when the direct currentis used alone. .By the use of asymmetrical alternating currents inaccordance with the present process, gold can be refined with' directcurrent densities of 1000 amperes or less to the square meter in asolution heated from 60 to 70 C., and containin only fromabout 1% to 2per cent. hydroch oric acid of 1.19 s ecific gravity, while in thetreatment with irect currents, there is required about four times asmuchacid, that is to say about 7 per cent. hydrochloric acid. On theother hand, the heating of the bath to a temperature-of about 60 or 70C.', can be dispensed with in the present process when the proportion ofby in the solution amounts to 7 er cent. or

frthe gold treated. Furthermore,

drochlonc acid 7 from, 600 to 1000 amperes to the square visahle; thatis to say, a density of the total "meter. I current corresponding tofrom I In the electrolytic treatment of gold in" U accordance w'th theold process ereinbefore-referred to, the 'heating-ofthe bath is I aJ1250*+1315 as5s 7o absolutely essential, as the direct current,ampemgmo the 'uare meter, 1 :thisbwse; when alone? m coldl f the Voltae of the direct current component though b l reqmslte denslty of isabout from 1 to 1.1 volts per bath and the mntffoo i 9 Square meter,\total voltage per'cell as indicatedfon a hot current component is notallowed to exceed \not more than l0 per cent, greater, is ad- P dupreclpitatimn fZ' Q gold wire oltam'eter, is about 1.4 volts. From viol'm'of P gi i m m 1 1mm this, the voltage of the alternati currentdarklbmwn 6 use 0 3 3 componentcan be'calculated as fol owsz, metricalcurrent notonly renders IMPOSSlblG 15 to increase the cathodic densityof the curt..= -,/(1.4 (1.1): .866 volts.

rent-as well as the anodic-density-of the curl a n% the ca acityofflfihe v y 3.0 e

rent, ma warm solut1on, -but also to refine mimosflt Wm aesim 1e toconslder 1.3

the gold my a cold sohmon the use of volts as the maximum voltage of thedirect etricalcurrentswhoseirect com o- V as mm P current, and 1 as 'themaxlmum voltage of -20 nenthas a density below 1000 amperes to'thethealternating current p bath. AS the f fz s f perfect y coherent 'dynamosare connected in series, the armaprecipi a es.

I n thel ractical operation of the process I fi i g g a g ggfiggzg ifigg f ifig fig fi p i g i gi gi g gg gg i? 2; current, i, The frequency ofthe alternatalternating current dynamo are connecte sg canpbe variedwmhlp the u l in genes a cimmt? mcludmg the 616cm? The streng hs andVoltage of the currents bath and the direct ailment dynamo 1S employedmay vary-widely accordin to the excited unt1l a polarized-direct currentam characterof the n to b fin d g If th '30 meter inserted mthe circuit,indicates the 01d contains than 8 e t 6 v desired strength of the directcurrent. P Gen thedensityiof' the direct current component can beadvantageously increased, or, if preferred, the strength of thealternating component relative to'the direct current com'ponent can bediminished.

It is found in ractice, that the ratio of the strength of t ealternating. current to I that of the directicurrentcannot be advantageously diminished below a certain limit. For instance, if thestrength of the alternating current becomes less than .707 of that ofthe direct current combined current will cease to be an alternatingcurrent' and wi become a mere undulatory direct current of eriodicallyvarying strength, in which case, the peculiar advantages of-the combinedIcurv rent hereinbefore set forth, are lost.

rent mtenslty 9 i i i In the practice of my process,Iordinarily Strengthof the direct 3 to bewequa work with a gold chlorid solution heated 50to the strength of the alternating current, from 60 to 700 andcoma-filingv at least as for example, to 200 amperes, the hot wire. 7per cent free hydnm one MEL In 15 ammeter must mdlcate cases gvhere togmucfh importance not attac e to ra i ity 0 treatment an one can 80000283 ampeljesf therefore be satisfied with a density of the Th totalVoltage f m Win h h p w r direct current between 500 and 1000amconsumptionis to be calculated, is indicated peres to the squaremeter, the treatment can. 12. by a hot wire voltameter.- Ihe degreevoltake place either at the tem erature inditage dependsof course, onthe strength of cated, the bath containing hy rochloric aci the totalcurrent. For example, if gold is in the proportion of from L} to 2 percent. ,being treated, which contains about 10 per of the solution, orthe treatment can take cent. of silver, a density of the direct currentplace with a cold solution in which case 7 12! component of about 1250amperes to the per cent. of hydrochloric acid as is emsquare meter,and adensity of the alternatployed, Instead of using'hydroc oric acid ingcurrentcomponent which isequal to, or in the gold chlorid solution, Imay substithis desired strength of the direct current is represented byi and if it is desired to work with' a virtual intensity of thealternating 35 current represented by 6,, the Virtual inten- 4 sity of Ythe total current obtained y the combined use of the two currents',canbe calculated according to the formula i a/i 01,.

This total current can only be measured b a hot wire instrument. Inaddition to the direct current ammeter,-a hot wire ammeter musttherefore also b inserted in the 45 asymmetrical current circuit. Thealternat ing current dynamo is then excited until the tute either Whollyor partially therefore trolyzing a solution of a gold salt by pass- 25chlorids such for example, as sodium 'ing an asymmetrical alternatingcurrent chlorid. therethrou h, with such gold or gold alloy i "In thepreferred practice of mg process, I as the anode. 4

5 emplo thinly rolled sheets of ne gold as process of electrolyticallyrefining catho es and introduce gold into the elecgold or gold, alloys,which consists in elec- 30 4 trolyte in the form of a gold chloridsolutrolyzing a solution containing'gold chlorid tion in proportion asthe gold contentof the and another chlorid with an excess of the 7 bathis diminished, in the o eration or the latter, by passing anasymmetrical alternatx 10 process. In refining gold w ich contains a incurrent therethrou h with such gold or material percentage of lead, mayadvango (1 alloy as the ano e. 35 tageously introduce sulfuric ac1d tothe bath, 3.. A process of electrolytically refining preferably in aquantity-approximately gold or gold alloys, which consists in elecequivalent to that of the free hydrochloric tro yzing a solution of oldchlorid, con-, 15 acid present. taining hydrochloric acig, by passin anWhile I somewhat prefer to em loy I asymmetrical alternating current tere- 4 hydro-chlor ic acid in the gold bath it 1s to through with suchgold or gold alloy as the be understood that I may advantageousl Ianode. 1 use a metal or other chlorid. and that suc In testimony whereofI have afiixed my 20 chlorid is the equivalent of hydro-chloricsignature 1n presence of two witnesses.

acid for use 1n my process. HEINRICH WOHLWILL.

I claim: Witnesses:

: 1. A process of electrolytically refining ERNEST H. L. MUMMENHOFF,

gold or gold alloys, which consists in 'elec- IDA OHR. HUFERMANN. 1

